1. Department of Neurosurgery, Mito Saiseikai General Hospital, Mito, Japan
2. Department of Neurosurgery, University of Tsukuba Hospital, Hitachi Social Cooperation Education Research Center/Hitachi General Hospital, Hitachi, Tsukuba, Japan
3. Department of Neurosurgery, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Japan
4. Department of Neurosugery, Ibaraki Seinan Iryo Center Hospital, Tsukuba, Japan
5. Department of Neurosurgery, NHO Mito Medical Center, Tsukuba, Japan
6. Department of Plastic Surgery, NHO Mito Medical Center, Tsukuba, Japan
7. Department of Neurosurgery, Institute of Medicine, University of Tsukuba, Tsukuba, Japan